Dehydrogenation and aromatization of C.sub.2 -C.sub.10 paraffins over a zeolite catalyst having the structure of ZSM-5, for example, requires a heat input of at least about 500 BTU per pound of feed at a reaction temperature of about 510.degree. C. to 705.degree. C. (950.degree. F. to 1300.degree. F.). The problem of transferring heat to the fluidized-bed process has been an obstacle to its commercial development. Methods known in the art to transfer heat to the fluidized-bed reaction zone include preheating the catalyst or positioning a heat exchanger in the fluidized catalyst bed. Preheating the catalyst separately to around 870.degree. C. (1600.degree. F.) undesirably accelerated catalyst deactivation.
In previous designs using a circulating inert gas heat transfer medium, the inert gas is heated by passing it through the tubes of a process furnace. The hot gas is then charged to a reactor heat exchanger positioned inside the fluidized-bed reaction zone. The hot inert gas is cooled as it passes through the reactor heat exchanger, indirectly transferring the endothermic heat of reaction to the surrounding fluidized bed and is then withdrawn from the reactor heat exchanger and typically cooled to about 38.degree. C. (100.degree. F.) to minimize the cost of compressing and recirculating the gas.